[Effect of Nitrogen Addition on Soil Fungal Diversity in a Degraded Alpine Meadow at Different Slopes].

This study proposed nitrogen addition experiments to analyze the effects of exogenous nitrogen addition on soil fungal diversity in alpine meadow. All the experiments were performed in degraded alpine meadow with two different slopes (gentle slope and steep slope) in Guoluo Prefecture of the Sanjiangyuan Region, and the sequence and analysis of ITS of soil fungi were performed using MiSeq PE250 sequencing technology. Comparative analysis was carried out with three nitrogen addition levels on soil fungal diversity in degraded grassland with different slopes, which included low nitrogen (LN, 2 g·m-2), middle nitrogen (MN, 5 g·m-2), and high nitrogen (HN, 10 g·m-2). The results showed that:① the distribution groups of fungi in the soil were Ascomycota, Basidiomycota, Mortierellomycota, and Glomomycota, and the dominant bacteria was Ascomycota. ② The dominant genera were Mortierella and Archaeorhizomyces, and there were no differences in response to different slopes and nitrogen addition levels. ③ A total of 95 genera (Gibberellum, Preussia, etc.) were identified and significantly differed between two different slopes (P<0.05). ④ Bacteria with a relative abundance less than 1% had significant differences in nitrogen addition at different levels on the same slope (P<0.05). 5 In addition, the analyses of α and ß diversities showed that soil fungal community structure was stable under different slopes and nitrogen addition levels. Exogenous nitrogen supplementation significantly improved the relative abundance of non-dominant fungal communities without destroying soil fungal community structure.

[Changes in Soil Bacterial Community Diversity in Degraded Patches of Alpine Meadow in the Source Area of the Yellow River].

MiSeq sequencing technology was used to investigate the bacterial compositions and diversities of active patch, non-active patch, recovered patch, and healthy alpine meadows so as to understand the changes in soil bacterial community diversity during altitude change and alpine meadow degradation. The relationship between bacterial diversity and environmental factors was analyzed using redundancy analysis (RDA). The results showed that the dominant bacterial phyla in the soil included Proteobacteria, Actinobacteriota, and Acidobacteriota in the study areas. The dominant bacterial genera that were identified via the MiSeq were RB41, Sphingomonas, and Bradyrhizobium. The relative abundance of these genera decreased with altitude increase and increased with the restoration progress of degraded patches but was significantly lower than that in the alpine meadow (P<0.05). The abundance of functional bacteria related to carbon fixation in degraded patches was higher than that in the healthy alpine meadow. The bacterial Chao1 index and species number in different types of degraded patches were significantly higher than those in the alpine meadow (P<0.05). The results of the RDA suggest that biological soil crust coverage and total nitrogen were the main influencing factors on dominant bacterial phyla at the altitude of 4013 m. Biomass, total nitrogen, and pH had a great influence on the dominant bacterial phyla at the altitude of 4224 m. Biomass and total potassium significantly affected the distribution of bacterial genera at the altitude of 4013 m. Sedge coverage and available nitrogen were the main influencing factors on bacterial dominant genera at the altitude of 4224 m. Biological soil crusts and pH had a great influence on bacterial diversities. The bacterial influence factors varied greatly at different altitude areas. Therefore, we should not only pay attention to the effect of alpine meadow degradation but also consider the effect of altitude in the study of bacterial diversity changes.

[Responses of Different Degradation Stages of Alpine Wetland on Soil Microbial Community in the Yellow River Source Zone].

MiSeq sequencing technology was used to analyze the microbial community diversity of soil in alpine wetlands to understand the degradation processes and environmental factors in these areas. The results showed that the severity of soil degradation changed the species diversity of soil microorganisms at the level of OTUs, and grass patches contained more species than frozen-thawing patches. The soil fungi species of OTUs changed significantly. The diversity indexes of bacteria (between the frozen-thawing patches and the grass patches) were higher than that of fungi. The dominant microbial species were consistent among different degradation stages. The dominant species of bacteria and fungi were Proteobacteria and RB41, and Ascomycota and Mortierella, respectively. The abundance of dominant microorganisms was significantly between un-degraded and heavily degraded areas, except for RB41 (P<0.05). The dominant microorganisms in the grass patches were more sensitive than those in the frozen-thawing patches. It was found that the main factors affecting the microbial community structure of soil were water content, organic carbon, microbial biomass carbon, microbial biomass nitrogen, and sedge coverage. Microbial diversity may decrease in heavily degraded alpine wetlands. Thus, the frozen-thawing patches and sedge species should be first protected, and the supplements of soil water content, soil organic carbon, microbial biomass carbon, and nitrogen should be strengthened for alpine wetland restoration.